Retinal malfunction, due to degenerative retinal diseases, is a leading cause of blindness and visual impairment. Implantation of a retinal prosthesis is a technology for restoring some useful vision in individuals suffering from retina-related blindness.
The retina is a multi-layered light-sensitive structure that lines the posterior, inner part of the eye. The retina contains photoreceptor cells, rods and cones, which capture light and convert light signals into neural signals transmitted through the optic nerve to the brain. Rods are responsible for light sensitive, low resolution black and white vision, whereas cones are responsible for sharp, high resolution color vision.
There are several types of retinal implants. For example, suprachoroidal implants are placed between the sclera and choroid of the eye. Additional types of retinal implants are epiretinal implants, which are placed on top of the retinal surface, and subretinal implants, which are placed under the retina between the photoreceptor layer and the retinal pigment epithelium, directly stimulating retinal cells and relying on the normal processing of the inner and middle retinal layers. Epiretinal designs typically include an electrode array directly stimulating ganglion cells and bypassing other retinal layers.
Some retinal implants include an internal imager, i.e., an intraocular camera. The internal imager effectively replaces the functionality of the native photoreceptor cells by capturing a scene in the direction of a subject's gaze.
In other cases, retinal implants rely on an external camera for capturing the visual information and replacing the functionality of the native photoreceptor cells.